Parse stderr for unadf banner.

Unadf does return 0 exit code always, even, if there was an issue in
either parsing image, mounting it or on any other issue. To be worst, it
always throw an banner to the stderr, so it cannot be used to check if
there was an error either.

As a workaround, let's check if there is a banner, strip it out and then
see if anything extra is on the stderr, so that it can be used to see if
there was any issues.

uadf

@@ -43,6 +43,10 @@ import tempfile
 import extfslib
 
 
+BANNER_PAT = re.compile(r'unADF v\d.\d : a unzip like for .ADF files, '
+                        r'powered by ADFlib (.*)\n\n')
+
+
 class UAdf(extfslib.Archive):
     """
     Class for interact with c1541 program and MC
@@ -111,6 +115,16 @@ class UAdf(extfslib.Archive):
         except (subprocess.CalledProcessError, OSError):
             pass
 
+    def _parse_banner(self, string):
+        match = BANNER_PAT.match(string)
+        if not match:
+            return
+
+        if match.end() == len(string):
+            return
+
+        return string[match.end():]
+
     def _map_name(self, name):
         if name.startswith(" "):
             new_name = "".join(["~", name[1:]])
@@ -123,8 +137,9 @@ class UAdf(extfslib.Archive):
         out = subprocess.run([self.ARCHIVER, self.CMDS['list'], self._arch],
                              capture_output=True, encoding="latin-1")
 
-        if out.stderr:
-            sys.stderr.write(out.stderr)
+        error_msg = self._parse_banner(out.stderr)
+        if error_msg:
+            sys.stderr.write(error_msg)
 
         for line in out.stdout.split("\n"):
             match = self.LINE_PAT.match(line)